I didn't look but it is either the outtake for the dam producing an effect like a toilet bowl flushing or it is at the bottom where all the fish congregate for the particles of food that have been flushed through the dam. Yellow, can you provide a clearer or more accurate explanation?

Glory Hole is usually used for the latter because of the fish, but I have heard it for the drainage swoosh also. I may need to go look for it now.

BTW, I think you two have your minds in the gutter.